Over the years, various systems have been devised for controlling engine-driven fire pumps. For instance, U.S. Pat. Nos. 3,786,689 A and 4,189,005 A to McLoughlin, as well as U.S. Pat. No. 5,888,051 A to McLoughlin et al., disclose apparatus and methods for controlling the pressure output from engine-driven centrifugal fire pumps. U.S. Pat. No. 7,040,868 B2 to McLoughlin et al. discloses systems for controlling pumping speed during discharge pressure fluctuations. U.S. Pat. No. 8,517,696 B2 to Mcloughlin et al. discloses a system for maintaining the fluid intake pressure of a pumping system above a preset value, while U.S. Patent Application Publication No. 2005/0061373 A1 to McLaughlin (sic) et al. discloses a system for maintaining the fluid intake pressure below a preset value.
One disadvantage of pump pressure governors that only control discharge pressure is that they are often unresponsive, or too slow to respond to, sudden pressure changes at the intake end of the system. Also, these types of governors are simply not able to reduce extremely high incoming pressure—for instance, pressure of 200 psi or higher—to a safe discharge pressure of approximately 100 psi. In addition, these type pressure control systems do not include any backup mechanisms for controlling the discharge pressure if the governor should fail.
A disadvantage of currently available systems that control intake pressure is that they are typically designed only for use with pressurized fluid sources. Such intake control systems are not useful when fire hydrants are unavailable and firefighters instead must rely on an unpressurized fluid source such as the over 500-gallon water tank which is normally carried on fire trucks, or an external source such as a lake or pond. Furthermore, such systems are not capable of siphoning foam or other additives from an auxiliary tank upstream of the pump.
The present invention addresses these problems as described below.